The present disclosure relates to detector circuits. Power amplifiers are widely used as circuits that amplify the power of a radio frequency signal when the radio frequency signal is going to be transmitted. In addition, a detector circuit is often used to detect the output power of a radio frequency signal output from a power amplifier.
For example, Japanese Unexamined Patent Application Publication No. 2008-148214 discloses a detector circuit that includes two transistors. Specifically, the detector circuit disclosed in FIG. 1 of the above-cited patent document includes a transistor Tr1 and a transistor Tr2. The collector voltage of the transistor Tr1 changes in accordance with the RF input power, and the collector voltage (detection voltage) of the transistor Tr2 changes in accordance with changes in the collector voltage of the transistor Tr1.
Incidentally, the current that flows through a transistor changes in the form of an exponential function with respect to the voltage supplied to the base thereof. Therefore, the detection voltage would typically change in the form of an exponential function with respect to the RF input power in the detector circuit disclosed in the above-cited patent document as well. In the detector circuit, the detection voltage may be linearly changed with respect to the RF input power.